The present invention relates to an electronic musical instrument of the type in which a musical tone is generated on the basis of a pitch extracted from an input waveform signal, and more particularly to an electronic string instrument such as an electronic guitar or a guitar synthesizer.
In recent days, there have been developed musical instruments of the type in which a pitch (frequency) is extracted from a waveform signal generated by a natural or conventional musical instrument, and under control of the extracted pitch, a sound source of an electronic circuitry is driven to artificially generate a sound such as a musical tone.
In this type of musical instrument, the pitch extraction still involves some problems to urgently be solved. Typical pitch extraction systems are a zero-cross point detection system and a peak detection system.
The zero-cross point detection system detects the time intervals between zero-cross points in the input waveform, and uses them as periods of the artificial sound. The input waveform frequently contains harmonics which should have been removed by filters such as low-pass filters. The detection system does not operate well for such input waveforms. If it is applied, the detected pitches contain many errors. To prevent the errors, complicated software processing techniques, for example, to check the duty of the input waveform, are required. It is technically difficult to realize this.
The peak-detection system detects maximum and minimum peak points of the input waveform signal, and sets and resets the flip-flop at the peak points, to generate a period signal, e.g., a rectangular wave signal. The peak detection system is disclosed in KOKOKU Nos. 57-37074 (corresponding to U.S. Pat. No. 4,117,757) and 57-58672, and KOKAI Nos. 55-55398, 55-152597 (Utility Model), and 61-26090.
The peak detection system determines the period of the artificial sound waveform by the time interval between the adjacent maximum peaks, for example. This feature causes reduction of the reliability of the detected pitches, and a slow response to frequency change of the input natural sound waveform. Use of the R-S flip-flop makes the instrument circuitry inflexible in generic use and makes it difficult to construct so-called intelligent musical instruments having data processing functions.
Other proposals for the pitch detection system are disclosed in KOKAI Nos. 55-87196 and 55-159495, and KOKOKU No. 61-51793.
KOKAI 55-87196 measures the period of the input natural sound waveform, and then converts the measured value into a frequency number, which in turn is sent to the sound source. No novel technical proposal for the period measurement is found in this KOKAI 55-87196 specification.
KOKAI 55-159495 and KOKOKU 61-51793 disclose a frequency stabilizing technique in which when the adjacent extracted periods are substantially the same, the sounding of the musical instrument starts. A sounding command is not sent to the sound source until at least two periods elapse. In this respect, these patent applications involve the response performance problem. To obtain a quick response, the sounding should start as soon as possible.
Utility Model KOKOKU No. 62-20871 (corresponding to U.S. Pat. No. 4,606,255) discloses another frequency stabilizing technique. In a string musical instrument, a vibration of one string affects the vibration of another string. In the extreme case, the latter vibrates resonating at the vibration frequency of the former. The proposal involves a high cost because mechanical parts are used, and yet it can only imperfectly remove the resonance.
As seen from the above prior art discussion, the known techniques are still immature and require improvement of, for example system stability, response and flexibility in use.